1. Field of the Invention
The present invention relates to a structure for connecting a window glass antenna with a feeder, and more particularly to a structure for respectively connecting primary and secondary antennas with an inner conductor of a coaxial cable serving as the feeder and with an outer conductor of the same.
2. Description of the Prior Art
There are some proposals of providing an antenna for transmission and reception of ultrashort waves on an automobile or a building window glass. For example, U.S. Pat. No. 4,721,964 discloses a vehicular window glass antenna system which has one feeding point connected to an inner conductor of a coaxial cable serving as a feeder. An outer conductor of the coaxial cable is grounded, through a lead such as a polyvinyl chloride wire, to a part of a vehicular body serving as a grounded conductor, the part being located near the feeding point. However, this type of antenna has the following drawbacks.
The outer conductor is not directly connected to the part of the vehicular body, but to the same through the lead. Therefore, the assembly work becomes complicated due to the installation of the lead. Furthermore, due to the provision of the lead, there is provided a certain inevitable transmission loss, thereby lowering reception gain.
JP-B (Utility Model) 51-16677 discloses a vehicular window glass antenna which is installed on a laminated glass. The laminated glass has two overlapped glass plates interposing therebetween an interlayer and an antenna. One of the glass plates has a through opening, for fully receiving therein a first terminal connected to the antenna. The first terminal is detachably connectable with a second terminal of a feeder. However, this type of antenna has the following drawback.
For installing the first terminal, it is necessary to drill the glass plate. This makes the assembly complicated and lowers strength of the laminated glass. Furthermore, this type of antenna can not be installed on a single glass plate.
JP-A (Utility Model) 4-5708 discloses a structure for connecting primary and secondary antennas with an inner conductor of a coaxial cable and with an outer conductor of the same through first and second terminals, respectively. The first terminal has a bent portion defining a space for tightly holding therein the inner conductor. The second terminal has a supporting portion which is semicylindrical in shape, and on which the outer conductor is supported. However, this connecting structure has the following drawbacks.
Because an upper half portion of an end portion of the outer conductor is exposed, upon soldering the outer conductor to the second terminal by a soldering iron, the outer conductor tends to be overheated by a direct abutment with the soldering iron. This overheat tends to damage an insulator disposed between the inner and outer conductors.
In view of the above-mentioned drawbacks, JP-A (Utility Model) 4-116411 discloses another structure for connecting primary and secondary antennas with an inner conductor of a coaxial cable and with an outer conductor of the same through first and second terminals, respectively. The second terminal has larger and smaller cylindrical portions. The smaller cylindrical portion has a through opening, and a certain amount of solder is adhered to the smaller cylindrical portion so as to fill up the through hole. In assembly, the coaxial cable is thrust into the larger and smaller cylindrical portions so as to hold an outer cover of the coaxial cable and the outer conductor of the same by the larger and smaller cylindrical portions, respectively. Then, a heated soldering iron is brought into abutment with the solder adhered to the smaller cylindrical portion so as to achieve soldering between the outer conductor and the smaller cylindrical portion. However, this structure has the following drawback.
The size of the through hole of the smaller cylindrical portion is not specified at all. Therefore, in case that its size is too small, it becomes difficult to check if a contact between the outer conductor and the small cylindrical portion is sufficiently achieved or not. If the soldering period becomes too long in this case, the outer cover and an insulator of the coaxial cable tend to be damaged. If the soldering period is too short, a contact between the outer conductor and the small cylindrical portion becomes poor.